netdev - Re: Weird DHCP related problems with net-next

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Date:	Wed, 10 Jun 2015 14:44:00 -0700
From:	Scott Feldman <sfeldma@...il.com>
To:	Florian Fainelli <f.fainelli@...il.com>
Cc:	Andrew Lunn <andrew@...n.ch>, Netdev <netdev@...r.kernel.org>,
	Jiri Pirko <jiri@...nulli.us>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: Weird DHCP related problems with net-next

On Tue, Jun 9, 2015 at 5:12 PM, Florian Fainelli <f.fainelli@...il.com> wrote:


> I see the problem now, DSA does not implement a port_obj_add callback,
> so when net/ipv4/fib_trie.c::switchdev_fib_ipv4_add() gets to call
> switchdev_port_obj_add, we return -EOPNOTSUPP, and take the error path
> in fib_table_insert thus not inserting the route for this interface.

Yup, that's the problem.

> Now when I restart the DHCP client, we end-up inserting the default
> route which is correct, still figuring out what is different here,
> probably the deletion of the routes by the DHCP client script first is
> the different condition.

After the first failure, ipv4.fib_offload_disabled is set, so the next
time switchdev_fib_ipv4_add() just returns 0 and the route is
installed.  That explains the one-off behavior.

> At any rate, since switchdev_fib_ipv4_add() returns something that make
> us take an error path in the fib_trie, something like this seems to fix
> it for me but I am not well versed enough into the IPv4 routing code to
> be 100% confident this is the right fix. Also, there are other callers
> of switchdev_port_obj_add() but a quick look seems to make them safe as
> they are only called for "offloading" capable hardware.

Your fix looks good to me.  The other users of
switchdev_port_obj_add() want to return -EOPNOTSUPP to user, so it's
just this one case for IPv4 fib insert/del where we'll want to treat
no support silently.  Are you going to resend as patch for net-next,
or should I?
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